Firstly, how do you or anyone else on this planet know what 90% of the world do or how much music is listened to on earbuds ?
Secondly, even supposing that that were true {and it will, unless you're God~in which case I don't think you'd be logging into HR.com !~never be known if it is } how many of that 90% are listening in the calm relaxed atmosphere of home or the car/vehicle or the hospital bed ? Earbuds, for the most part, are for listening on the move.........
In my job I constantly run into people arriving for work in lifts with their MP3 players and sometimes I ask them whether they prefer loudspeakers or earbuds. In 4 years, only one person has said they prefer buds.
Now, this may or may not demonstrate anything, but in reality, any mix will translate to earbuds because that is what earbuds, like headphones, do. They aren't and never were designed as an end or sound medium in themselves, but rather, to carry directly to your ears what is already there in the playing machine. So if you were to "mix for earbuds", you'd actually be narrowing your focus, whereas by mixing for the actual format {that is, mono, stereo or 5.1, rather than the speaker, which, essentially buds are} you cater for everyone and every single combination of listening in one fell swoop.